THETA-MICROSCOPY ALLOWS PHASE REGULATION IN 4PI(A)-CONFOCAL 2-PHOTON FLUORESCENCE MICROSCOPY

A solution for the phase problem in 4Pi(A)-confocal fluorescence micro scopy has been found by observation orthogonal to the optical axis. Th ree-dimensional intensity distributions for 4Pi;(A)-confocal microscop y and confocal theta microscopies are calculated. The evaluations in t he focal region show that the volume integrals of the 4Pi(A)-point spr ead functions are strongly attenuated when the interference is not con structive ill the geometrical focus. This results in a phase dependent fluorescence intensity signal with a modulation of up to 48% with whi ch the relative phase of the interfering wavefronts can be measured an d regulated.